This application is based on and claims the priority under 35 U.S.C. xc2xa7119 of German Patent Application 101 23 285.3, filed on May 12, 2001, the entire disclosure of which is incorporated herein by reference.
The invention relates to an igniter element for igniting a pyrotechnic charge or active mass, on a circuit carrier arrangement having an ignition electronics assembly thereon, for example for triggering a gas generator of a passenger or occupant protection device, such as an airbag, in a motor vehicle.
Igniter elements for igniting pyrotechnic charges typically comprise a wire that can be ignited by applying an electric voltage thereto. This ignitable wire is arranged or mounted on a circuit carrier arrangement, on which there is further arranged an ignition electronic assembly, which provides the necessary ignition energy and which carries out communication with a databus, for example as disclosed in German Patent DE 196 10 799 C1. It is also known, and becoming more prevalent, to use a layer of ignitable material instead of an ignitable wire, whereby in the prior art such an ignitable layer has always been deposited on the circuit carrier arrangement, for example as disclosed in published European Patent Application EP 0,555,651 B1.
To achieve a further integration of the overall igniter arrangement, German Patent DE 199 40 201 C1 discloses using the surface of a circuit component, for example preferably the surface of an ignition capacitor, as a circuit carrier substrate, on which conductor paths are deposited, and further circuit components including an ignition layer are arranged, to achieve an extremely compact overall construction.
All of the above mentioned igniter arrangements, however, suffer the disadvantage or problem, that a manufacturer of such igniter arrangements must carry out not only the steps of mounting components on the circuit carrier arrangement, but also the steps of forming or depositing the ignition bridge layer, and often also steps of manufacturing or mounting the entire pyrotechnic components. Especially the pyrotechnic zone including the pyrotechnic components of such an igniter arrangement requires especially high safety demands and special equipment and processes for mounting and installing the various components. As a result, the manufacturer must fulfill all applicable safety requirements and must be equipped to carry out various diverse technological processes, including dangerous processes in the field of pyrotechnics.
It is further known in the art to provide a spatial or structural separation of the pyrotechnic zone from the electronic zone in an igniter arrangement, for example as disclosed in the German Patents DE 40 02 088 C1 and DE 198 36 280 C1. In these references, a protective wall is provided as a structural separation element between the pyrotechnic zone and the ignition electronics zone. Additional electrical connections must be established through the protective wall to provide the necessary electrical connection between the two zones on opposite sides of the wall. Therefore, by providing such a protective wall, the electronic assembly may be well-protected and in some cases can even be manufactured independently of the pyrotechnic zone, but it is not possible for the manufacturer of the electronic assembly to completely test the functionality thereof, because the ignition bridge element of course must be arranged in the pyrotechnic zone and must be connected to the rest of the electronic circuitry for being able to test the functionality thereof.
In view of the above, it is an object of the invention to provide an igniter element arrangement that is easy to manufacture and mount, and that allows a separation of the pyrotechnic components from the electronic components in the fabrication process and technology, while still allowing a complete functional testing of the ignition arrangement to be carried out. The invention further aims to avoid or overcome the disadvantages of the prior art, and to achieve additional advantages, as apparent from the present specification.
The above objects have been achieved according to the invention in an ignition arrangement including a circuit carrier, an ignition electronics assembly mounted on the circuit carrier, an igniter element arrangement mounted on the circuit carrier, and a pyrotechnic charge operatively contacting or connected to the igniter element arrangement. The invention particularly involves an improvement of the igniter element arrangement comprising an igniter element that is mounted on an igniter element carrier body which is separate and distinct from the circuit carrier. The igniter element carrier body comprises contacts or conductors for establishing electrical contact between the igniter element itself and the circuit carrier. The igniter element carrier body is preferably configured and dimensioned with the same shape, size, format, contact configuration, and the like, as other standard electronic components of the ignition electronics assembly, so that the overall igniter element arrangement can essentially be handled and mounted as a standardized electronic component, in the same manner as any other standardized electronic component.
The basic underlying idea of the invention is particularly not to arrange or mount the igniter element directly on the circuit carrier, but rather to provide the igniter element on a carrier body that is separate from the circuit carrier, and then to mount this carrier body on the circuit carrier. This idea may be directly contrary to the general demands for reducing the size and the complexity of igniter arrangements and circuits, but it achieves considerable advantages in the manufacturing and the functional reliability.
The carrier body for carrying the igniter element is preferably a monolithic or integral one-piece component of an electrically non-conductive, heat resistant (i.e. able to withstand the temperatures that arise during ignition and burning of the pyrotechnic charge), and poorly thermally conducting material (i.e. a substantially thermally insulating material, which means a material that is at least as thermally insulating as, and preferably more thermally insulating than, the circuit carrier itself), for example glass or ceramic. The igniter element may be formed from any suitable ignitable material deposited as a layer on the surface of the carrier body, and similarly, the necessary electrical contacts can be established by depositing metallized conductor paths on the surface of the carrier body in any conventionally known manner.
According to the invention, this igniter element carrier body can be designed, embodied and arranged in a standardized manner, with respect to its dimensions, configuration, and electrical contacts, in consideration of the corresponding parameters required by the component mounting devices and the electrical contacting devices, e.g. respective robots, used in the production of the ignition electronics assembly on the circuit carrier. In other words, the igniter element carrier body can be handled and mounted on the circuit carrier as a totally normal standardized circuit component. The pyrotechnically active electrical ignition layer itself on the carrier body is still not particularly a safety concern, as long as it does not come into contact with the pyrotechnic charge or active mass. Thus, the entire circuit carrier with all of the components mounted thereon, including the igniter element arrangement, can be mounted and assembled in normal electronics assembly halls using normal electronics assembly equipment, and can then be transported and stored as a finished assembly without any specialized safety measures, and may further, at any time, be completely tested as to its electrical functionality.
Moreover, the manufacturer of the finished circuit carrier with all of the components mounted thereon can obtain the igniter element arrangement as an externally supplied pre-fabricated component from a pyrotechnic specialist. Thus, the manufacturer of the overall circuit arrangement does not need to have and operate special equipment or processes for forming the igniter element or mounting it on its carrier body or mounting the carrier body on the substrate. In other words, the igniter element arrangement becomes an independent component that is commercially available as such, which leads to corresponding economies in the manufacturing of the overall ignition arrangement, as well as allowing specialization of the distinct aspects required for the manufacturing of the overall ignition arrangement.
As a further advantage, the carrier body acts as a protection or protective mass between the circuit carrier on the one hand, and the igniter element and the pyrotechnic charge on the other hand. Thus, the interposed carrier body to some extent protects the circuit carrier from the influences (e.g. thermal and mechanical loads) of the burning of the pyrotechnic charge.
The carrier body furthermore makes it possible to achieve a variable configuration or orientation of components during the mounting and assembly, especially with reference to the orientation of the circuit carrier relative to the pyrotechnic charge. Namely, the igniter element or ignition bridge itself does not necessarily need to be provided on the top of the carrier body, but rather can be provided on a side surface of the carrier body, so that an arrangement and orientation of the circuit carrier extending perpendicularly away from the pyrotechnic charge is easily achievable, without requiring complicated mounting receivers or special contacts for the igniter element.